Electronic ballasts

Abstract

A lighting system (1) having a high intensity discharge lamp (16) and an electronic ballast having a variable frequency generator (10) which is arranged to vary the frequency of the ballast output over a range of frequencies having a minimum frequency of 400 kHz; a reactance is included in a joint operating circuit (22) in and between the ballast generator (10) and lamp (16) such that the circuit resonate to provide a starting voltage for the lamp at or above the minimum frequency. The arrangement inhibits lamp flickering and improves overall lamp and system efficiency.

What is claimed is:  
     
       1. A thermionic lighting system comprising: 
       a high intensity discharge lamp,  
       an electronic ballast having a regulated alternating current power output,  
       a joint operating circuit included in and between the ballast and the lamp,  
       the ballast having a variable frequency generator which is arranged to vary a frequency of the ballast output over a range of frequencies, with a minimum frequency of 400 kHz,  
       the circuit having a reactance such that the circuit is arranged to be resonant to provide a starting voltage for the lamp at or above the minimum frequency.  
     
     
       2. The thermionic lighting system as claimed in  claim 1  wherein the ballast is arranged to regulate the power output to the lamp by varying the frequency of the ballast output. 
     
     
       3. The thermionic lighting system as claimed in  claim 1  wherein a maximum frequency of the range is such that the power output is sufficient to maintain operation of the lamp. 
     
     
       4. The thermionic lighting system as claimed in  claim 1  wherein the range of frequencies is from 400 kHz to 1,500 kHz. 
     
     
       5. The thermionic lighting system as claimed in  claim 3  wherein the ballast power output is regulated so that the output provides a constant power to the lamp when it is running in a steady state, and a higher current during a starting phase of the lamp. 
     
     
       6. The thermionic lighting system as claimed in  claim 1  wherein the alternating current has a substantially sinusoidal waveform with a harmonic distortion of less than 40%. 
     
     
       7. The thermionic lighting system as claimed in  claim 6  wherein the substantially sinusoidal waveform has a harmonic distortion of less than 15%. 
     
     
       8. The thermionic lighting system as claimed in  claim 1  wherein the reactance comprises a series arrangement of an inductance and a capacitor where the output frequency and the value of the reactance is arranged so that the output frequency is above a resonant frequency of the reactance. 
     
     
       9. The thermionic lighting system as claimed in  claim 8  wherein the ballast is arranged to provide the alternating current output by alternate switching of at least two inverter output transistors driven by means for providing a discontinuous alternating waveform, the waveform containing a period within every half cycle when neither output transistor conducts. 
     
     
       10. A thermionic lighting system comprising: 
       a high intensity discharge lamp,  
       an electronic ballast having a regulated alternating current power output,  
       a joint operating circuit included in and between the ballast and the lamp,  
       the ballast having a variable frequency generator which is arranged to vary a frequency of the ballast output over a range of frequencies, with a minimum frequency of 400 kHz,  
       the circuit having a reactance such that the circuit is arranged to be resonant to provide a staring voltage for the lamp at or above the minimum frequency,  
       wherein the reactance comprises a series arrangement of an inductance and a capacitor where the output frequency and the value of the reactance is arranged so that the output frequency is above a resonant frequency of the reactance, and  
       the output power is arranged to pass through a capacitor in series with the lamp, the value of capacitance being sufficiently small to limit a current flow, through the lamp at a frequency of the electrical power input to the ballast, to less than 30 mA.  
     
     
       11. A thermionic lighting system comprising: 
       a high intensity discharge lamp,  
       an electronic ballast having a regulated alternating current power output,  
       a joint operating circuit included in and between the ballast and the lamp,  
       the ballast having a variable frequency generator which is arranged to vary a frequency of the ballast output over a range of frequencies, with a minimum frequency of 400 kHz,  
       the circuit having a reactance such that the circuit is arranged to be resonant to provide a starting voltage for the lamp at or above the minimum frequency,  
       wherein a connection to the lamp is arranged so that the lamp can be replaced, and a capacitance is placed in a parallel current path to the lamp, the capacitance being arranged such that disconnection of the lamp from the ballast output disconnects the capacitance from the ballast, the variable frequency generator being so arranged to sweep over a pre-determined range of frequencies to produce by means of a resonant circuit including the said capacitor a specific high frequency high voltage output to ignite the lamp.  
     
     
       12. A thermionic lighting system comprising: 
       a high intensity discharge lamp,  
       an electronic ballast having a regulated alternating current power sinusoidal waveform output,  
       a joint operating circuit included in and between the ballast and the lamp,  
       the ballast having a variable frequency generator which is arranged to vary a frequency of ballast output over a range of frequencies, with a minimum frequency of 400 kHz,  
       the circuit having a reactance such that the circuit is arranged to be resonant to provide a starting voltage for the lamp at or above the minimum frequency.